Treat string for regex use

Question

I've got my own indexOf function

private static int indexOf(String target, String pattern){

    Pattern p = Pattern.compile(pattern);

    Matcher matcher = p.matcher(target);

    if(matcher.find()){

        return matcher.start();

    }

    return -1;
}

This function takes in a user provided pattern and to see if the pattern exists within the target String. Sometimes a user could include regex characters like *** hello world in the String and this causes the function to return a Exception in thread "main" java.util.regex.PatternSyntaxException: Dangling meta character '*' error.

How can I treat the user generated String to overcome errors like these?

Are they supposed to be able to include regex characters used *properly*? — Explosion Pills, May 10 '13 at 22:16
@ExplosionPills They are not.. I want the regex char's to be treated the same as `s` `a` `b` etc. — Skizit, May 10 '13 at 22:18
http://stackoverflow.com/questions/60160/how-to-escape-text-for-regular-expression-in-java — Michał Ziober, May 10 '13 at 22:19

score 0 · Answer 1 · edited Jun 20 '20 at 09:12

Use Pattern.quote

Pattern p = Pattern.compile(Pattern.quote(pattern));

Note: this assumes that it isn't a real regex being passed in.

public static String quote(String s)

Returns a literal pattern String for the specified String. This method produces a String that can be used to create a Pattern that would match the string s as if it were a literal pattern.

Metacharacters or escape sequences in the input sequence will be given no special meaning.

Treat string for regex use

1 Answers1